Method for fabricating a semiconductor device and semiconductor device

ABSTRACT

The present invention discloses a method for fabricating a semiconductor device, comprising: providing a translucent portion; forming a covering layer comprised of one or more metals on the translucent portion by vapor deposition; providing kinetic energy to the covering layer for forming a periodic mask; forming a periodic structure on the translucent portion by using the periodic mask.

CROSS-REFERENCES TO RELATED APPLICATIONS

This Application claims the benefit of priority and is a Continuationapplication of the prior International Patent Application No.PCT/JP2005/015530, with an international filing date of Aug. 26, 2005,which designated the United States, and is related to the JapanesePatent Application No. 2004-251468, filed Aug. 31, 2004, the entiredisclosures of all applications are expressly incorporated by referencein their entirety herein.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method for fabricating asemiconductor device and a semiconductor device.

(2) Description of Related Art

A semiconductor light-emitting element formed with a low-temperaturedeposition buffer layer (1986, H. Amano, N. Sawaki, I. Akasaki, and Y.Toyoda: Appl. Phys. Lett., 48 (1986) 353) has been proposed in therelated art as this type of semiconductor light-emitting element. Asemiconductor light-emitting element to which p-type conductivitycontrol (1989, H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki: Jpn. J.Appl. Phys. 28 (1989) L2112) and n-type conductivity control (1991, H.Amano and I. Akasaki: Mat. Res. Soc. Ext, Abst., EA-21 (1991) 165) areapplied has also been proposed. A semiconductor light-emitting elementcreated by applying a highly efficient light emitting layer fabricatingmethod (1991, N. Yoshimoto, T. Matsuoka, T. Sasaki, and A. Katsui, Appl.Phys. Lett., 59 (1991) 2251) has also been proposed.

FIG. 13 shows an exemplary constitution of a group III nitridesemiconductor light-emitting element serving as an example of asemiconductor light-emitting element to which the techniques describedabove are applied. In the drawing, a group III nitride semiconductorlight-emitting element 1 comprises a sapphire substrate 2, and alow-temperature deposition buffer layer 3 is deposited on top of thesapphire substrate 2. An n-GaN cladding layer 4, a GaInN light-emittinglayer 5, a p-AlGaN barrier layer 6, and a p-GaN contact layer 7 aredeposited in succession on the low-temperature deposition buffer layer3. A p-electrode 8 is deposited on the uppermost p-GaN contact layer 7,and an n-electrode 9 is deposited on the n-GaN layer, thereby formingthe group III nitride semiconductor light-emitting element 1.

In a group III nitride semiconductor light-emitting element, representedby the semiconductor light-emitting element constituted as describedabove, blue light, green light, and white light can be emitted at highintensity. In other types of semiconductor light-emitting element suchas AlGaInP and AlGaAs, for example, a substantially identical layerstructure can be produced using a substrate having an appropriatelattice constant, and thus a high light-emission efficiency can berealized.

Even in a semiconductor light-emitting element having highlight-emission efficiency, if the efficiency with which light isextracted to the outside of the semiconductor light-emitting element ispoor, the overall energy conversion efficiency of the semiconductorlight-emitting element is also poor. Hence, improvement of the lightextraction efficiency is important. One of the causes of poor lightextraction efficiency is a semiconductor refractive index which islarger than the refractive index of air. When the refractive index ofthe semiconductor is larger than the refractive index of air, a largeamount of the light emitted by the light-emitting later is reflectedtotally, thereby becoming sealed in the interior of the semiconductorlight-emitting element.

To solve this problem, a method of molding a semiconductorlight-emitting element using an epoxy resin or the like having arefractive index between the refractive index of the semiconductorlight-emitting element and the refractive index of air is known (seeSemiconductor Elements, Revision, Tetsuro Ishida and Azuma Shimizu,Corona, 1980, for example). A method of improving the light extractionefficiency by forming a large number of protrusions at a peak period of500 nm or more on the surface layer of the semiconductor light-emittingelement is also known (see Japanese Unexamined Patent ApplicationPublication 2003-174191, for example). According to the formerconstitution, the extreme refractive index difference between thesemiconductor light-emitting element and air can be reduced, enabling areduction in total reflection and an improvement in the light extractionefficiency. In the latter constitution, the emitted light is reflecteddiffusely by the surface irregularities and can therefore be extracted,enabling an improvement in the light extraction efficiency.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a method for fabricating a semiconductordevice, comprising: providing a translucent portion; forming a coveringlayer comprised of one or more metals on the translucent portion byvapor deposition; providing kinetic energy to the covering layer forforming a periodic mask; and forming a periodic structure on thetranslucent portion by using the periodic mask.

Another optional aspect of the present invention provides a method forfabricating a semiconductor device, wherein: the periodic mask is usedas an etching mask.

One optional aspect of the present invention provides a method forfabricating a semiconductor device, wherein: the periodic mask is usedas a crystal growth mask.

Another optional aspect of the present invention provides a method forfabricating a semiconductor device, wherein: the kinetic energy isprovided for selective reduction in effective volume of the coveringlayer.

One optional aspect of the present invention provides a method forfabricating a semiconductor device, wherein: the covering layer iscomprised of Au.

Another optional aspect of the present invention provides a method forfabricating a semiconductor device, further including: forming a highlyreflective metallic layer on the periodic mask.

One optional aspect of the present invention provides a semiconductordevice fabricated by a method, comprising: providing a translucentportion; forming a covering layer comprised of one or more metals on thetranslucent portion by vapor deposition; providing kinetic energy to thecovering layer for forming a periodic mask; and forming a periodicstructure on the translucent portion by using the periodic mask.

Another optional aspect of the present invention provides asemiconductor device, comprising: a translucent portion; and a periodicstructure comprised of a plurality of juts distributed randomly on asurface of the translucent portion, with the periodic structure havingspace period lengths with a first standard deviation that is smallerthan 20% of average length of the space periods.

One optional aspect of the present invention provides a semiconductordevice, wherein: the average length of the space periods is shorter thantwice of an average optical wavelength of a light through thetranslucent portion.

Another optional aspect of the present invention provides asemiconductor device, wherein: the light through the translucent portionis emitted by a semiconductor layer included in the semiconductordevice.

One optional aspect of the present invention provides a semiconductordevice, wherein: an average height of the juts is greater than theaverage optical wavelength.

Another optional aspect of the present invention provides asemiconductor device, wherein: a second standard deviation in heights ofthe juts is smaller than 20% of the average height of the juts.

One optional aspect of the present invention provides a semiconductordevice, wherein: the translucent portion is a substrate.

Another optional aspect of the present invention provides asemiconductor device, wherein: the translucent portion substrate iscomprised of SiC.

One optional aspect of the present invention provides a semiconductordevice, wherein: the periodic structure is formed on a surface on anopposite side of the substrate to a side on which the semiconductorlayer is deposited.

Another optional aspect of the present invention provides asemiconductor device, wherein: a group III nitride semiconductor layeris deposited between a substrate and the semiconductor layer, and theperiodic structure is formed on an interface between the substrate andthe group III nitride semiconductor layer.

One optional aspect of the present invention provides a semiconductordevice, wherein: the translucent portion is a sealing portion that sealsthe semiconductor device.

Another optional aspect of the present invention provides asemiconductor device, wherein: the sealing portion completely seals thesemiconductor device.

One optional aspect of the present invention provides a semiconductordevice, wherein: the sealing portion partially seals the semiconductordevice.

Another optional aspect of the present invention provides asemiconductor device, wherein: the juts are formed in a substantiallypyramidal shape.

One optional aspect of the present invention provides a semiconductordevice, wherein: a highly reflective metallic layer is formed on theperiodic structure.

Another optional aspect of the present invention provides asemiconductor device, wherein: the highly reflective metallic layerconstitutes an electrode.

One optional aspect of the present invention provides a semiconductordevice, comprising: a first semiconductor layer having a first side anda second side with the first semiconductor layer having a translucentproperty; a low temperature deposition buffer layer on the first side ofthe first semiconductor layer; a cladding layer on the low temperaturedeposition buffer layer; a light emitting layer on the cladding layer; abarrier layer on the light emitting layer; a contact layer on thebarrier layer, with the light emitting layer, the barrier layer, and thecontact layer selectively etched for exposing part of the claddinglayer; a n-type electrode on the exposed part of the cladding layer; anda p-type electrode on the contact layer.

Another optional aspect of the present invention provides asemiconductor device, wherein: the second side of the firstsemiconductor layer is comprised of a periodic structure that iscomprised of a plurality of juts.

One optional aspect of the present invention provides a semiconductordevice, wherein: an average distribution space period of the juts isgreater than a standard deviation of the distribution space period.

One optional aspect of the present invention provides a semiconductordevice, wherein: an average heights of the juts is greater than astandard deviation of the average heights of the juts.

One optional aspect of the present invention provides a semiconductordevice, wherein: the juts are formed by etching the second side of thefirst semiconductor layer using a periodic mask that is resistant toetching medium.

These and other features, aspects, and advantages of the invention willbe apparent to those skilled in the art from the following detaileddescription of preferred non-limiting exemplary embodiments, takentogether with the drawings and the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that the drawings are to be used for the purposesof exemplary illustration only and not as a definition of the limits ofthe invention. Throughout the disclosure, the word “exemplary” is usedexclusively to mean “serving as an example, instance, or illustration.”Any embodiment described as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other embodiments.

Referring to the drawings in which like reference character(s) presentcorresponding parts throughout:

FIG. 1 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a first embodiment;

FIG. 2 is an exemplary perspective view of a periodic structureaccording to the first embodiment;

FIG. 3 is an exemplary histogram showing the light output of thesemiconductor light-emitting element to which the present invention isapplied;

FIG. 4 is an exemplary graph showing the relationship between opticaltransmittance and an average period;

FIG. 5 is an exemplary process diagram of a periodic structure accordingto the first embodiment;

FIG. 6 is an exemplary process diagram of the periodic structureaccording to the first embodiment;

FIG. 7 is an exemplary process diagram of the periodic structureaccording to the first embodiment;

FIG. 8 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a second embodiment;

FIG. 9 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a third embodiment;

FIG. 10 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a fourth embodiment;

FIG. 11 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a fifth embodiment;

FIG. 12 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a sixth embodiment; and

FIG. 13 is an exemplary schematic diagram of a semiconductorlight-emitting element according to a conventional example.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently preferred embodimentsof the invention and is not intended to represent the only forms inwhich the present invention may be constructed and or utilized.

(1) First Embodiment

FIG. 1 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element as a semiconductor deviceaccording to a first embodiment of the present invention. In thedrawing, a semiconductor light-emitting element 10 is constituted by asubstrate 11 as a translucent portion, a low-temperature depositionbuffer layer 12, a cladding layer 13, a light-emitting layer 14, abarrier layer 15, a contact layer 16, a p-electrode 17, and ann-electrode 18, all of which are formed in a substantially plate-shapedform. In the drawing, the plate-form substrate 11 constituting thelowermost layer is consisted of SiC. The low-temperature depositionbuffer layer 12 consisted of AlGaN (a group III nitride semiconductor),the cladding layer 13 consisted of n-GaN, the light-emitting layer 14consisted of GaInN, the barrier layer 15 consisted of p-AlGaN, and thecontact layer 16 consisted of p-GaN are deposited in succession onto thefront side surface of the substrate 11. The plate-form p-electrode 17 isdeposited onto the contact layer 16 constituting the uppermost layer,and the n-electrode 18 is deposited on the cladding layer 13. Periodicirregularities are formed on the back side of the substrate 11. Notethat the section extending from the cladding layer 13 consisted of n-GaNto the contact layer 16 consisted of p-GaN constitutes a light-emittingportion of the present invention.

FIG. 2 shows an exemplary back side (the opposite surface to the surfaceon which the light-emitting portion is deposited) of the substrate 11seen diagonally. In the drawing, the back surface of the substrate 11takes an indented form created by forming a large number ofsubstantially conical juts 11 a, 11 a, 11 a, . . . thereon so as toprotrude downward from the back side of the substrate 11. Note that thejuts 11 a, 11 a, 11 a, . . . are distributed periodically in atwo-dimensional direction on the back surface of the substrate 11, andare referred to collectively as a periodic structure A1. The averageheight of the juts 11 a, 11 a, 11 a, . . . is approximately 300 nm, andthe standard deviation thereof is approximately 20 nm. Note that theheights of the juts 11 a, 11 a, 11 a, . . . are assumed to be thedifference between the peak heights and base heights of the juts 11 a,11 a, 11 a, . . . . The average distribution space period of the juts 11a, 11 a, 11 a, . . . is approximately 200 nm, and the standard deviationof this distribution space period is approximately 15 nm. Note that theinterval between the peaks of adjacent juts 11 a, 11 a, 11 a, . . . willbe referred to as the distribution space period of the juts 11 a, 11 a,11 a, . . . or the average period of the periodic structure A1.

In this constitution, light can be emitted from the light-emitting layer14 when a voltage is applied in a forward bias direction between thep-electrode 17 and n-electrode 18 of the semiconductor light-emittingelement 10. In the light-emitting layer 14, light is emitted at awavelength corresponding to the band gap thereof In the light-emittingportion of this embodiment, the average optical wavelength of the lightis approximately 220 nm. Note that the optical wavelength is a valueobtained by dividing the actual wavelength by the refractive index.Further, the wavelength of the light emitted by the light-emitting layer14 is distributed within a wavelength bandwidth of several tens of nm,and the average value thereof is approximately 220 nm. The substrate 11,low-temperature deposition buffer layer 12, cladding layer 13, barrierlayer 15, and contact layer 16 each possess a translucency, and hencethe light emitted by the light-emitting layer 14 can be extracted fromthe back side of the substrate 11. In other words, the back surface ofthe substrate 11 serves as a light extraction surface of thesemiconductor light-emitting element 10, and the light that is extractedfrom the extraction surface can be used for illumination and so on.

The light emitted from the light-emitting layer 14 penetrates theperiodic structure Al formed on the back surface of the substrate 11,and is discharged into the air on the exterior of the semiconductorlight-emitting element 10. The refractive index of the light isdifferent in the air on the exterior of the semiconductor light-emittingelement 10 and in the substrate 11 consisted of SiC, and hence theinterface between the periodic structure A1 and the air forms areflective surface. Accordingly, light which enters the interfacebetween the periodic structure A1 and the air at an angle of incidencewhich exceeds a critical angle may be reflected on the interface andbecome sealed in the interior of the semiconductor light-emittingelement 10. However, in the present invention, the average period(approximately 200 nm) of the periodic structure A1 is smaller than theoptical wavelength (approximately 220 nm) of the emitted light, andhence the majority of the light that reaches the periodic structure A1feels a refractive index between that of the air and that of thesubstrate 11.

The refractive index on the periodic structure A1 may be considered tovary in accordance with the surface area ratio of the air which isdistributed over a sliced surface obtained by slicing the periodicstructure A1 in a parallel direction to the back surface of thesubstrate 11. In actuality, the air and the SiC of the substrate 11 aredistributed non-uniformly over the sliced surface, but this non-uniformdistribution exists in a shorter period than the average opticalwavelength, and hence the majority of the light feels an intermediaterefractive index that is dependent on the surface area ratio. On thesliced surface near the base of the periodic structure A1, the surfacearea ratio occupied by the air is small, and hence the refractive indexof the substrate 11 contributes greatly at the height near the base ofthe periodic structure A1. Conversely, on the sliced surface near thepeak of the periodic structure A1, the surface area ratio occupied bythe air is large, and hence the refractive index of the air contributesgreatly at the height of the peak of the periodic structure A1. Inshort, the periodic structure A1 may be considered to have a refractiveindex (effective refractive index) which converges gradually toward therefractive index of the air from the refractive index of the substrate11 as the light advances more deeply in the height direction of theperiodic structure A1.

The transition of the refractive index corresponding to the height ofthe periodic structure A1 depends on the shape of the juts 11 a, 11 a,11 a, . . . . For example, when the juts 11 a, 11 a, 11 a, . . . inclinelinearly, as in this embodiment, the refractive index may be consideredto vary in a continuous parabola. As a result, dramatic variation in therefractive index on the periodic structure A1, which constitutes theinterface between the substrate 11 and the air, can be prevented, andlight can be prevented from being reflected by the periodic structureA1. Note, however, that the shape of the juts 11 a, 11 a, 11 a, . . . isnot limited to a conical shape, and the effects of the present inventioncan be exhibited with other shapes. In other words, any shape having asectional area which varies gradually in accordance with the height maybe employed, and accordingly the protrusions may be provided in theshape of triangular pyramids, quadrangular pyramids, hemispheres, ortrapezoids, for example.

The height (approximately 400 nm) of the periodic structure A1 in thisembodiment is greater than the average optical wavelength of the light(approximately 220 nm) and the average period (approximately 200 nm),and hence the angle at which the incline of the juts 11 a, 11 a, 11 a, .. . intersects the substrate 11 can be set to a comparatively largeangle (near 90 degrees). By forming the periodic structure A1 to behigh, dramatic variation in the refractive index can be prevented evenin relation to light which enters the formation surface of the periodicstructure A1 at a shallow angle. Further, by forming the periodicstructure A1 to be high, the surface area ratio varies gently inaccordance with the height of the periodic structure A1, and thegradient of linear variation in the refractive index can be reduced. Inother words, dramatic variation in the refractive index can besuppressed, and a high reflection prevention ability can be realized.

FIG. 3 illustrates exemplary effects of the present invention in theform of a histogram. In the drawing, the abscissa shows a ratio betweenthe light output of the present invention, formed as shown in FIG. 1,and the light output of a conventional semiconductor light-emittingelement formed as shown in FIG. 13. The ordinate shows the number ofsamples corresponding to each light output ratio. Note that the lightoutput was checked on 30 semiconductor light-emitting elements accordingto the present invention. It was found that with the samples to whichthe present invention was applied, a light output between 3.4 and 4.6times (mode: 3.8 times) greater than the conventional semiconductorlight-emitting element was obtained. It was also found that electricenergy input into the semiconductor light-emitting element 10 could beextracted as optical energy with substantially no loss.

As noted above, the effects of the present invention are exhibited whenthe average period of the periodic structure A1 is smaller than theaverage optical wavelength of the light, but by setting the standarddeviation of the distribution space period of the juts 11 a, 11 a, 11 a,. . . within 20% (preferably within 10%) of the average period of theperiodic structure A1, the effects of the present invention can beexhibited with certainty. Further, the standard deviation of thedistribution space period of the juts 11 a, 11 a, 11 a, . . . ispreferably as small as possible, but there is no need to form the juts11 a, 11 a, 11 a, . . . regularly in a lattice shape or the like, forexample. Note, however, that the juts 11 a, 11 a, 11 a, . . . arepreferably distributed on the back surface of the substrate 11 in atwo-dimensional direction in order to prevent anisotropy in effects ofthe present invention. The periodic structure A1 may of course be formedin striped form, even though anisotropy occurs as a result. Further,variation in the height of the juts 11 a, 11 a, 11 a, . . . ispreferably held within 20% (more preferably within 10%) of the average.

FIG. 4 shows an exemplary transmittance on the interface between thesubstrate 11 and the air in the form of a graph. In the diagram, theordinate shows the optical transmittance and the abscissa shows theaverage period of the periodic structure A1. Note that the averageperiod of the periodic structure A1 shown on the abscissa is expressedas a multiple of the average optical wavelength (approximately 220 nm)of the emitted light. As is evident from the diagram, the transmittanceimproves in a region where the average period of the periodic structureA1 is approximately 500 nm or less, i.e. 3 times the average opticalwavelength (approximately 220 nm) or less. In a region where the averageperiod of the periodic structure A1 is double the average opticalwavelength or less, a particularly high light extraction efficiency canbe realized in the semiconductor light-emitting element 10. By makingthe average period of the periodic structure A1 equal to or less thanthe average optical wavelength, as in this embodiment, an opticaltransmittance of almost 100% can be realized. In other words, theaverage period of the periodic structure A1 is preferably as small aspossible.

The light emitted from the light-emitting layer 14 has an averageoptical wavelength of approximately 220 nm but a wavelength bandwidth ofseveral tens of nm, and hence as the average period of the periodicstructure A1 decreases, the proportion of the emitted light that has asmaller optical wavelength than the period of the periodic structure A1increases. Accordingly, the optical transmittance can be raisedgradually from the region in which the average period of the periodicstructure A1 is between 2 and 3 times greater than the average opticalwavelength of the emitted light, and brought close to 100% in the regionwhere the average period of the periodic structure A1 is equal to orlower than the average optical wavelength of the emitted light.

Next, a fabricating method for the semiconductor light-emitting element10 will be described. First, the substantially plate-form substrate 11is prepared. Note that at this point in time, the periodic structure A1is not formed on the back side of the substrate 11. The low-temperaturedeposition buffer layer 12 is formed at a predetermined thickness bygrowing AlGaN uniformly on the front side of the substrate 11 using ametal-organic chemical vapor deposition method. In a similar fashion,the cladding layer 13 is formed on the low-temperature deposition bufferlayer 12 and the light-emitting layer 14 is formed on the cladding layer13. The barrier layer 15 is then formed on the light-emitting layer 14,whereupon the contact layer 16 is formed by growing p-GaN on the barrierlayer 15.

After depositing the various layers in the manner described above, acovering layer 20 is formed on the back side of the substrate 11 byapplying Au evenly thereto as a covering material through vapordeposition, as shown in FIG. 5 (vapor deposition). Various vapordeposition methods may be applied to deposit the Au. For example, an EBvapor deposition apparatus which performs vapor deposition by heatingthe Au in a vacuum to cause the Au to transpire may be used. Further,the Au may be applied using a wet method, for example, as long as the Aucan be distributed with a certain degree of uniformity over the backside of the substrate 11. Note that in this embodiment, vapor depositionis performed such that the film thickness of the covering layer 20 isapproximately 50 Å (50 m⁻¹⁰).

After forming the covering layer 20, the semiconductor light-emittingelement 10 is heated in an oven or the like (kinetic energy providingstep for selective reduction in effective volume of the covering layer30). At this time, the covering layer 20 formed on the back side of thesubstrate 11 is heated evenly to approximately 180° C., for example,over the entire surface of the covering layer 20. In so doing, kineticenergy can be applied to each of the Au atoms constituting the coveringlayer 20, and as a result, the Au atoms can be agglomerated on the backside surface of the substrate 11. Then, by cooling the semiconductorlight-emitting element 10, a large number of Au particles 30, 30, 30, .. . can be distributed over the back side surface of the substrate 11,as shown in FIG. 6. The covering layer 20 is formed at an even filmthickness and kinetic energy is applied evenly over the entire surface,as described above, and therefore the cohesive energy of the Au atomsmay be considered uniform over the entire back side of the substrate 11.Accordingly, the Au particles 30, 30, 30, . . . can be distributed ateven periods over the back side surface of the substrate 11, as shown inFIG. 6.

Note that the distribution space period of the Au particles 30, 30, 30,. . . may be controlled in accordance with the heating temperature, thefilm thickness of the covering layer 20, and so on. In this embodiment,the covering layer 20 having a film thickness of approximately 50 Å (50m⁻¹⁰) is heated to approximately 180° C., whereby the Au particles 30,30, 30, . . . can be distributed in an average period of approximately200 nm. To increase the distribution space period of the Au particles30, 30, 30, . . . , the heating temperature may be raised or the filmthickness of the covering layer 20 may be increased, for example.Conversely, to reduce the distribution space period of the Au particles30, 30, 30, . . . , the heating temperature may be lowered or the filmthickness of the covering layer 20 may be decreased. Further, as long askinetic energy can be applied to the covering layer 20 to the extentthat the Au atoms can be agglomerated, the periodic Au particles 30, 30,30, . . . may be formed using a method other than heating. For example,kinetic energy may be applied to the covering layer through ionirradiation, electron irradiation, and so on. Note that the Au particles30, 30, 30, . . . form a periodic pattern having an average period whichis equal to or lower than the average optical wavelength, and hence as awhole, the Au particles 30, 30, 30, . . . constitute a periodic mask ofthe present invention (mask forming step).

After forming the Au particles 30, 30, 30, . . . so as to be distributedperiodically over the back side surface of the substrate 11 in themanner described above, the back side of the substrate 11 is etchedusing a reactive ion etching apparatus (etching step). In thisembodiment, CF₄ gas is used as an etching medium. Needless to say,another etching gas may be used, or etching may be performed using anetching liquid. The etching resistance of Au to CF₄ gas is higher thanthe etching resistance of SiC to CF₄ gas, and hence the SiC may beetched selectively. The etching direction is perpendicular to the backsurface of the substrate 11, and etching may be performed only on theparts of the back side surface of the substrate 11 to which the Auparticles 30, 30, 30, . . . are not adhered.

More specifically, etching may be performed using the periodic maskconstituted by the large number of Au particles 30, 30, 30, . . . as anetching resist. In so doing, the periodic structure A1 may be formed asshown in FIG. 8 (periodic structure forming step). Note that byincreasing the etching speed, etching typically progresses perpendicularto the back surface of the substrate 11, and as a result the angle ofincline of the juts 11 a, 11 a, 11 a, . . . becomes almost perpendicularto the back surface of the substrate 11. Conversely, by reducing theetching speed, side etching is performed, and hence the angle of inclineof the juts 11 a, 11 a, 11 a, . . . becomes an acute angle in relationto the back surface of the substrate 11.

By performing etching using the periodic mask in this manner, the shapeof the periodic structure A1 can be controlled to a desired shape.Furthermore, as long as etching is not performed excessively, the peaksof the juts 11 a, 11 a, 11 a, . . . can be aligned in height. As aresult, variation in the height of the juts 11 a, 11 a, 11 a, . . . canbe reduced. Note that the amount of side etching may be increasedintentionally to remove the Au particle 30, as shown on the thirdprotruding portion 11 a from the left in FIG. 7. Furthermore, theetching conditions may be set such that the Au particle 30 is removed byetching. Note that in this embodiment, the performance of thesemiconductor light-emitting element 10 is not greatly diminished evenwhen the Au particles 30, 30, 30, . . . remain in the interior of thesemiconductor light-emitting element 10. However, the performance may bediminished depending on the material of the covering layer, and in sucha case the periodic mask is preferably removed.

The material of the periodic mask is not limited to Au, and any materialmay be used as long as the etching resistance to the etching medium isgreater than that of the substrate. Specifically, the etching selectionratio between the periodic mask and the substrate is preferably at least0.1, and more preferably at least 1. Examples of periodic mask materialsthat are effective in relation to CF₄ gas include Ga, In, Al, Cu, Ag,Ni, Pt, Pd, SiN, SiO₂, or an insulator. An appropriate periodic maskmaterial is selected in accordance with the etching medium, and hence itgoes without saying that other periodic mask materials may be applied.Note, however, that when atom or molecule agglomeration is employed inthe periodic mask forming step, as in this embodiment, a gatherablecovering material such as Au must be selected.

Furthermore, in this embodiment the periodic mask is formed usingagglomeration of the covering layer, but a periodic mask may be formedusing another method. For example, a periodic mask pattern may be formedusing a stepper employing an excimer laser. Alternatively, a periodicmask pattern may be formed by subjecting a photosensitive mask materialto electron beam exposure and so on or two-beam interference exposure.

After forming the periodic structure A1 in the manner described above,the p-electrode 17 and n-electrode 18 are formed and the semiconductorlight-emitting element 10 is packaged. Note that the cladding layer 13may be exposed by selectively etching the uniformly depositedlight-emitting layer 14, barrier layer 15, and contact layer 16 to formthe n-electrode 18, or the cladding layer 13 may be exposed byselectively growing the light-emitting layer 14, barrier layer 15, andcontact layer 16 in advance to form the n-electrode 18. Further, theperiodic structure A1 may be formed after forming the n-electrode 17 andn-electrode 18.

Further, the various layers may be formed on the front side of thesubstrate 11 after forming the periodic structure A1 on the back side ofthe substrate 11 in advance. Moreover, the substrate 11 may be consistedof a material other than SiC as long as it possesses a translucency. Forexample, a sapphire substrate, a GaN substrate, a Ga₂O₃ substrate, a GaNsubstrate, and so on may be applied. Needless to say, the presentinvention is also applicable to another type of semiconductorlight-emitting element such as AlGaInP or AlGaAs, for example. Note thatthe average optical wavelength of the emitted light varies according tothe type of light-emitting layer, but as long as the periodic structureA1 is formed in a period which is double the average optical wavelengthor less (preferably no greater than the average optical wavelength), ahigh light extraction efficiency can still be realized.

(2) Second Embodiment

FIG. 8 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element as a semiconductor deviceaccording to a second embodiment of the present invention. In thedrawing, a semiconductor light-emitting element 110 is constituted by asubstrate 111 as a translucent portion, a low-temperature depositionbuffer layer 112, a cladding layer 113, a light-emitting layer 114, abarrier layer 115, a contact layer 116, a p-electrode 117, and ann-electrode 118, all of which are formed in a substantially plate-shapedform. The plate-form substrate 111 constituting the lowermost layer isconsisted of SiC. The low-temperature deposition buffer layer 112consisted of AlGaN, the cladding layer 113 consisted of n-GaN, thelight-emitting layer 114 consisted of GaInN, the barrier layer 115consisted of p-AlGaN, and the contact layer 116 consisted of p-GaN aredeposited in succession onto the front side surface of the substrate111. A periodical structure A2 constituted by periodically arranged Auparticles 130, 130, 130, . . . is provided on the uppermost contactlayer 116, and a highly reflective metallic layer consisted of Cu andserving as the p-electrode 117 is deposited onto the contact layer 116formed with the periodical structure A2. The back side of the substrate111 is a flat surface, and the n-electrode 118 is deposited thereon.

With this constitution, light can be emitted from the light-emittinglayer 114 by applying a voltage to the semiconductor light-emittingelement 110 in a forward bias direction. In the light-emitting layer114, light is emitted in accordance with the band gap thereof, and theaverage optical wavelength of the light is approximately 220 nm. Thesubstrate 111, low-temperature deposition buffer layer 112, claddinglayer 113, barrier layer 115, and contact layer 116 each possess atranslucency, and hence the light emitted by the light-emitting layer114 can be extracted from the back side of the substrate 111. In otherwords, the back side of the substrate 111 serves as a light extractionsurface of the semiconductor light-emitting element 110, and the lightthat is extracted from the extraction surface can be used forillumination and so on.

Meanwhile, the upper surface of the contact layer 116 is covered by thep-electrode 117, which is consisted of highly reflective Cu, and byreflecting the emitted light, the light is prevented from leaking fromthe p-electrode 117 side. The reflected light can be extracted from thelight extraction surface and used for illumination and so on. By formingthe periodical structure A2, diffuse reflection can be promoted, andhence the reflectance on the interface between the contact layer 116 andthe p-electrode 117 can be improved. As a result, the amount of lightthat is ultimately extracted from the light extraction surface of thesemiconductor light-emitting element 110 can be increased, enabling animprovement in the light extraction efficiency to approximately 1.3times the normal light extraction efficiency.

Next, a fabricating method for the semiconductor light-emitting element110 will be described. First, the substantially plate-form substrate 111is prepared. The low-temperature deposition buffer layer 112 is thenformed at a predetermined thickness by growing AlGaN uniformly on thefront side of the substrate 111 using a metal-organic chemical vapordeposition method. In a similar fashion, the cladding layer 113 isformed on the low-temperature deposition buffer layer 112 and thelight-emitting layer 114 is formed on the cladding layer 113. Thebarrier layer 115 is then formed on the light-emitting layer 114,whereupon the contact layer 116 is formed by growing p-GaN on thebarrier layer 115.

After depositing the various layers in the manner described above, asimilar covering layer to that of FIG. 5 is formed on the surface of thecontact layer 116 by applying Au evenly thereto as a covering materialthrough vapor deposition. Various vapor deposition methods may beapplied to deposit the Au. For example, an EB vapor deposition apparatuswhich performs vapor deposition by heating the Au in a vacuum to causethe Au to transpire may be used. Further, the Au may be applied using awet method, for example, as long as the Au can be distributed with acertain degree of uniformity over the surface of the contact layer 116.Note that in this embodiment, vapor deposition is performed such thatthe film thickness of the covering layer is approximately 50 Å (50m⁻¹⁰).

After forming the covering layer, the semiconductor light-emittingelement 110 is heated in an oven or the like. At this time, the coveringlayer formed on the surface of the contact layer 116 is heated toapproximately 180° C., for example. In so doing, kinetic energy can beapplied to each of the Au atoms constituting the covering layer, and asa result, the Au atoms can be agglomerated on the surface of the contactlayer 116. Then, by cooling the semiconductor light-emitting element110, a large number of Au particles 130, 130, 130, . . . can bedistributed over the surface of the contact layer 116. As describedabove, the covering layer is formed at an even film thickness, and thecohesive energy of the Au atoms which agglomerate during heating may beconsidered uniform over the surface of the contact layer 116.Accordingly, the Au particles 130, 130, 130, . . . can be distributed ina uniform periodical form on the surface of the contact layer 116,similarly to FIG. 6.

After forming the Au particles 130, 130, 130, . . . so as to bedistributed periodically over the surface of the contact layer 116 inthe manner described above, Cu is applied to the contact layer 116 andthe Au particles 130, 130, 130, . . . through vapor deposition (highlyreflective metallic layer forming step). An EB vapor depositionapparatus or the like may be used here to deposit the Cu, or Cu may beapplied to the surface of the contact layer 116 using a method otherthan vapor deposition. In the initial stage of vapor deposition, the Auparticles 130, 130, 130, . . . form irregularities on the surface of thecontact layer 116, but as vapor deposition progresses, the gaps betweenthe Au particles 130, 130, 130, . . . are filled by the Cu such thateventually a flat surface is formed as the p-electrode 117. In otherwords, a highly reflective metallic layer is formed as the p-electrode117 so as to contact the interface with the periodical structureconstituted by the Au particles 130, 130, 130, . . . .

The substrate of this embodiment may be consisted of a material otherthan SiC as long as it possesses a translucency. For example, a sapphiresubstrate, a GaN substrate, a Ga₂O₃ substrate, a GaN substrate, and soon may be applied. Needless to say, the present invention is alsoapplicable to another type of semiconductor light-emitting element suchas AlGaInP or AlGaAs, for example. Note that the average opticalwavelength of the emitted light varies according to the type oflight-emitting layer, but as long as the periodic structure A2 is formedat a period which is no greater than the average optical wavelength, ahigh light extraction efficiency can still be realized. Furthermore, inthis embodiment Cu is cited as an example of the material used to formthe highly reflective metallic layer, but the highly reflective metalliclayer may be consisted of Rh, Ag, Al, Ni, Pt, Cu, an alloy thereof, andso on. By using the highly reflective metallic layer as an electrode, areduction in the number of fabricating steps can be realized. However,the highly reflective metallic layer and electrode may be formedseparately.

(3) Third Embodiment

FIG. 9 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element as a semiconductor deviceaccording to a third embodiment. In the drawing, a semiconductorlight-emitting element 210 is constituted by a substrate 211, alow-temperature deposition buffer layer 212, a cladding layer 213, alight-emitting layer 214, a barrier layer 215, a contact layer 216, ap-electrode 217, and an n-electrode 218, all of which are formed in asubstantially plate-shaped form. The plate-form substrate 211constituting the lowermost layer is consisted of SiC. Thelow-temperature deposition buffer layer 212 consisted of AlGaN, thecladding layer 213 consisted of n-GaN, the light-emitting layer 214consisted of GaInN, the barrier layer 215 consisted of p-AlGaN, and thecontact layer 216 consisted of p-GaN are deposited in succession ontothe front side surface of the substrate 211. A periodical structure A3(with an average period of approximately 200 nm and an average height of400 nm) is formed by a large number of juts protruding upward from theuppermost contact layer 216. The p-electrode 217 consisted of Cu isdeposited onto the periodical structure A3, and the n-electrode 218 isdeposited onto the back side of the substrate 211.

With this constitution, light can be emitted from the light-emittinglayer 214 by applying a voltage to the semiconductor light-emittingelement 210 in a forward bias direction. In the light-emitting layer214, light is emitted in accordance with the band gap thereof, and theaverage optical wavelength of the light is approximately 220 nm. Thesubstrate 211, low-temperature deposition buffer layer 212, claddinglayer 213, barrier layer 215, and contact layer 216 each possess atranslucency, and hence the light emitted by the light-emitting layer214 can be extracted from the back side of the substrate 211. In otherwords, the back surface of the substrate 211 serves as a lightextraction surface of the semiconductor light-emitting element 210, andthe light that is extracted from the extraction surface can be used forillumination and so on.

Meanwhile, the upper surface of the contact layer 216 is covered by thep-electrode 217 consisted of highly reflective Cu, and by reflecting theemitted light, the light can be prevented from leaking from thep-electrode 217 side. The reflected light can be extracted from thelight extraction surface and used for illumination and so on. By formingthe periodical structure A3, diffuse reflection can be promoted, andhence the reflectance on the interface between the contact layer 216 andthe p-electrode 217 can be improved. As a result, the amount of lightthat is ultimately extracted from the light extraction surface of thesemiconductor light-emitting element 210 can be increased, enabling animprovement in the light extraction efficiency.

Next, a fabricating method for the semiconductor light-emitting element210 will be described. First, the substantially plate-form substrate 211is prepared. The low-temperature deposition buffer layer 212 is thenformed at a predetermined thickness by growing AlGaN uniformly on thefront side of the substrate 211 using a metal-organic chemical vapordeposition method. In a similar fashion, the cladding layer 213 isformed on the low-temperature deposition buffer layer 212, and thelight-emitting layer 214 and barrier layer 215 are formed on thecladding layer 213. The contact layer 216 is then formed by growingp-GaN on the barrier layer 115.

After depositing the various layers in the manner described above, theperiodic structure A3 is formed on the surface of the contact layer 216.A similar method to that of the first embodiment may be applied to formthe periodic structure A3, and hence description thereof has beenomitted here. Once the periodic structure A3 has been formed, Cu isapplied to the surface of the contact layer 216 through vapordeposition. In the initial stage of vapor deposition, the periodicstructure A3 forms irregularities on the surface of the contact layer216, but as vapor deposition progresses, the gaps in the periodicstructure A3 are filled by the Cu such that eventually a flat surface isformed as the p-electrode 217. In the previous embodiment, the number offabricating steps can be reduced by employing the Au particles as theperiodic structure A2. In this embodiment, on the other hand, the shapeof the periodic structure A3 can be controlled by forming the periodicstructure A3 using the Au particles as a periodic mask.

(4) Fourth Embodiment

FIG. 10 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element as a semiconductor deviceaccording to a fourth embodiment. In the drawing, a semiconductorlight-emitting element 310 is constituted by a substrate 311, alow-temperature deposition buffer layer 312, a cladding layer 313, alight-emitting layer 314, a barrier layer 315, a contact layer 316, ap-electrode 317, and an n-electrode 318, all of which are formed in asubstantially plate-shaped form. The plate-form substrate 311constituting the lowermost layer is consisted of SiC. Thelow-temperature deposition buffer layer 312 consisted of AlGaN, thecladding layer 313 consisted of n-GaN, the light-emitting layer 314consisted of GaInN, the barrier layer 315 consisted of p-AlGaN, and thecontact layer 316 consisted of p-GaN are deposited in succession ontothe front side surface of the substrate 311. The p-electrode 317 isdeposited onto the contact layer 316 constituting the uppermost layer,and the n-electrode 318 is deposited onto the back side of the substrate311.

An indented periodic structure A4 is formed periodically on the frontsurface side of the substrate 311 as a translucent portion, and thelow-temperature deposition buffer layer 312 and cladding layer 313 areformed in alignment with periodic structures 311 a, 311 a, 311 a, . . .. The front surface side of the cladding layer 313 is flat, and all ofthe layers above the cladding layer 313 are formed to be flat.

By forming the indented periodic structure A4 periodically on the frontsurface side of the substrate 311 in this manner, reflectance on theinterface between the substrate 311 and low-temperature depositionbuffer layer 312 can be reduced. The refractive index of the substrate311 is different to the refractive index of the low-temperaturedeposition buffer layer 312, but by means of the periodic structure A4,dramatic variation in the refractive index can be suppressed. Further,by forming a layer having a thin film thickness such as thelow-temperature deposition buffer layer 312, the irregular form of theperiodic structure A4 is maintained, and hence the interface between thelow-temperature deposition buffer layer 312 and the cladding layer 313deposited thereon can also be formed in a periodically indented shape.Accordingly, reflectance on the-interface between the low-temperaturedeposition buffer layer 312 and the cladding layer 313 can also bereduced.

By forming the periodic structure on a plurality of interfaces in thismanner, the light extraction efficiency can be further improved.Further, by forming a thin film layer (the low-temperature depositionbuffer layer 312) on the periodic structure A4 at a thickness which doesnot flatten the periodic structure A4, an irregular shape can bemaintained on the surface of the thin film layer (low-temperaturedeposition buffer layer 312). Accordingly, by depositing an upper layer(the cladding layer 313) on the surface of the thin film layer(low-temperature deposition buffer layer 312) a periodic structure canbe formed on the interface between the thin film layer (low-temperaturedeposition buffer layer 312) and the upper layer (cladding layer 313).In other words, steps for forming periodic structures individually oneach interface need not be performed, and a semiconductor light-emittingelement having a high light extraction efficiency can be manufactured ata low fabricating cost.

Next, a fabricating method for the semiconductor light-emitting element310 will be described. First, the substantially plate-form substrate 311is prepared. Next, the periodic structure A4 is formed on the front sideof the substrate 311. A similar method to the method of forming theperiodic structure A1 on the back side of the substrate 11 in the firstembodiment may be applied to form the periodic structure A4, and hencedescription thereof has been omitted here. After forming the periodicstructure A4, the low-temperature deposition buffer layer 312 is formedin a shape corresponding to the periodic structure A4 by growing AlGaNuniformly on the front side of the substrate 311 using a metal-organicchemical vapor deposition method.

The cladding layer 313 is then formed by growing n-GaN on the front sideof the low-temperature deposition buffer layer 312 using a metal-organicchemical vapor deposition method. When the cladding layer 313 has beenformed to a certain extent, the recessed portions of the periodicstructure A4 are buried by the n-GaN such that ultimately, a flatsurface is formed. Once the flat surface of the cladding layer 313 hasbeen formed, the light-emitting layer 314 is formed on the claddinglayer 313, and the barrier layer 315 is grown on the light-emittinglayer 314. The contact layer 316 is then formed by growing p-GaN on thebarrier layer 315. The p-electrode 317 is deposited onto the uppermostcontact layer 316, and the n-electrode 318 is deposited onto the backside of the substrate 311.

(5) Fifth Embodiment

FIG. 11 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element as a semiconductor deviceaccording to a fifth embodiment of the present invention. In thedrawing, a semiconductor light-emitting element 410 is constituted by asubstrate 411, a low-temperature deposition buffer layer 412, a claddinglayer 413, a light-emitting layer 414, a barrier layer 415, a contactlayer 416, a p-electrode 417, and an n-electrode 418, all of which areformed in a substantially plate-shaped form. The plate-form substrate411 constituting the lowermost layer is consisted of SiC. Thelow-temperature deposition buffer layer 412 consisted of AlGaN, thecladding layer 413 consisted of n-GaN, the light-emitting layer 414consisted of GaInN, the barrier layer 415 consisted of p-AlGaN, and thecontact layer 416 consisted of p-GaN are deposited in succession ontothe front side surface of the substrate 411. The p-electrode 417 isdeposited onto the contact layer 416, and the n-electrode 418 isdeposited onto the back side of the substrate 411. Note that thep-electrode 417 is consisted of transparent mesh-form Ni/Au or the like,and is capable of transmitting light. The p-electrode 417 may employ atransparent electrode made of Ga₂O₃, ZnO, ITO, or the like, as long asit is capable of transmitting light to a certain extent.

The substrate 411, low-temperature deposition buffer layer 412, claddinglayer 413, light-emitting layer 414, barrier layer 415, contact layer416, and n-electrode 418 are deposited in flat plate form. An indentedperiodic structure A5 is formed periodically on the surface of thecontact layer 416, and the p-electrode 417 is deposited onto theperiodic structure A5 so as to follow the indentations of the periodicstructure A5. The surface of the p-electrode 417 is formed so as tomaintain the irregularities of the periodic structure A5.

By forming the indented periodic structure A5 periodically on the frontside of the contact layer 416 in this manner, reflectance on theinterface between the contact layer 416 and the p-electrode 417 can bereduced. The refractive index of the contact layer 416 is different tothe refractive index of the p-electrode 417, but by means of theperiodic structure A5, dramatic variation in the refractive index can besuppressed. Further, by forming a layer having a thin film thicknesssuch as the p-electrode 417, the irregular form of the periodicstructure A5 is maintained, and hence the interface between thep-electrode 417 and the air can also be formed in a periodicallyindented shape. Accordingly, reflectance on the interface between thep-electrode 417 and the air can also be reduced.

Next, a fabricating method for the semiconductor light-emitting element410 will be described. First, the substantially plate-form substrate 411is prepared. Next, the low-temperature deposition buffer layer 412 isformed by growing AlGaN uniformly on the front side of the substrate 411using a metal-organic chemical vapor deposition method. The claddinglayer 413 is then formed by growing n-GaN on the front side of thelow-temperature deposition buffer layer 412 using a metal-organicchemical vapor deposition method. The light-emitting layer 414 is thenformed on the cladding layer 413, and the barrier layer 415 is formed onthe light-emitting layer 414. The contact layer 416 is then formed bygrowing p-GaN on the barrier layer 415.

The indented periodic structure A5 is then formed periodically on thecontact layer 416 as a translucent portion. A similar method to themethod used to form the periodic structure A1 on the back side of thesubstrate 11 in the first embodiment may be applied to form the periodicstructure A5, and hence description thereof has been omitted here. Afterforming the periodic structure A5, the p-electrode 417 is deposited ontothe periodic structure A5 through coating or vapor deposition.Meanwhile, the n-electrode 418 is deposited onto the back side of thesubstrate 411.

(6) Sixth Embodiment

FIG. 12 shows an exemplary outline of the structure of a group IIInitride semiconductor light-emitting element according to a sixthembodiment. In the drawing, a hemispherical dome-shaped sealing portion60 is formed, and the semiconductor light-emitting element 10 of thefirst embodiment is buried within the interior of the sealing portion 60such that the light extraction surface is oriented upward on the papersurface. The sealing portion 60 is consisted of a synthetic resin suchas transparent epoxy resin, and is capable of transmitting light emittedfrom the semiconductor light-emitting element 10 to the outside. Thesurface of the sealing portion 60 as a translucent portion is formedwith a periodically indented periodic structure A6. A similar method tothe method used to form the periodic structure A1 on the back side ofthe substrate 11 in the first embodiment may be applied to form theperiodic structure A6, and hence description thereof has been omittedhere.

By forming the indented periodic structure A6 periodically on thesurface of the sealing portion 60 in this manner, reflectance on theinterface between the sealing portion 60 and the outside air can bereduced. The refractive index of the air is different from that of thesealing portion 60, but by means of the periodic structure A6, dramaticvariation in the refractive index can be suppressed. Note that thesemiconductor light-emitting element 10 may be sealed in the sealingportion 60 in various ways, and only the light extraction surface may besealed in the sealing portion 60. In this case also, the efficiency withwhich light is extracted to the outside of the sealing portion 60 can beimproved by forming the periodic structure A6 on the surface of thesealing portion 60.

SUMMARY

According to the present invention described above, by forming theperiodic structure A1 on the light extraction surface of thesemiconductor light-emitting element 10 in a period which is double theaverage optical wavelength of the light or less, the refractive indexdifference on the light extraction surface can be reduced. As a result,reflection on the light extraction surface can be prevented, enablingthe realization of a high light extraction efficiency. Furthermore, afine periodic mask can be formed by heating an Au thin film, andtherefore the periodic structure A1 can be formed easily and at lowcost.

Further, a semiconductor light-emitting element may be formed bycombining the various embodiments appropriately. For example, thesemiconductor light-emitting elements of the first through fifthembodiments may be sealed inside the sealing portion 60 of the sixthembodiment. Further, a semiconductor light-emitting element may beformed by combining the constitution of the first embodiment with theconstitution of the second or third embodiment, for example. Accordingto this constitution, high reflectance can be realized on the oppositesurface of the light-emitting portion to the light extraction surfacewhile realizing high transmittance on the light extraction surface, andhence the light extraction efficiency can be improved synergistically.Although the invention has been described in considerable detail inlanguage specific to structural features and or method acts, it is to beunderstood that the invention defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as preferred forms ofimplementing the claimed invention. Therefore, while exemplaryillustrative embodiments of the invention have been described, numerousvariations and alternative embodiments will occur to those skilled inthe art. For example, the material of the substrate can be changed. Suchvariations and alternate embodiments are contemplated, and can be madewithout departing from the spirit and scope of the invention.

1. A semiconductor device, comprising: a translucent portion having afirst semiconductor layer that has a first side and a second side; thefirst side of the first semiconductor layer is comprised of a firstuniformly distributed periodic structure; a light emitting portion thatcontacts the first side and is comprised of: a thin coating of lowtemperature deposition buffer layer deposited onto the first side thatmimics and parallels the first uniformly distributed periodic structure;the low temperature deposition buffer layer includes a second bufferside that contacts the first side of the first semiconductor layer,forming a second uniformly distributed periodic structure; the lowtemperature deposition buffer layer further includes a first buffer sideforming a third uniformly distributed periodic structure, with the firstbuffer side contacting a second cladding side of a cladding layer, withthe second cladding side forming a fourth uniformly distributed periodicstructure as a result of contact with the first buffer side of the lowtemperature deposition buffer layer; a light emitting layer thatcontacts a first cladding side of the cladding layer; a barrier layerthat contacts the light emitting layer; a contact layer that contactsthe barrier layer; a p-electrode that contacts the contact layer; and an-electrode that contacts the second side of the first semiconductorlayer; with the first, the second, the third, and the fourth uniformlydistributed periodic structure having an effective refractive index thatconverges gradually towards a second refractive index from a firstrefractive index as light emitted advances and penetrates more deeply ina height direction of one uniformly distributed periodic structuretowards another uniformly distributed periodic structure, which improvestransmittance of light by suppressing variations in first and secondrefractive indexes; with light ultimately extracted from the second sideof the first semiconductor layer.